# Copyright 2008-2020 pydicom authors. See LICENSE file for details.
"""Define the Sequence class, which contains a sequence DataElement's items.

Sequence is a list of pydicom Dataset objects.
"""
from copy import deepcopy
from typing import cast, overload, Any
from collections.abc import Iterable, MutableSequence
import weakref
import warnings

from pydicom import config
from pydicom.dataset import Dataset
from pydicom.multival import MultiValue


def validate_dataset(elem: object) -> Dataset:
    """Check that `elem` is a :class:`~pydicom.dataset.Dataset` instance."""
    if not isinstance(elem, Dataset):
        raise TypeError("Sequence contents must be Dataset instances.")

    return elem


class Sequence(MultiValue[Dataset]):
    """Class to hold multiple :class:`~pydicom.dataset.Dataset` in a
    :class:`list`.

    This class is derived from :class:`~pydicom.multival.MultiValue`
    and as such enforces that all items added to the list are
    :class:`~pydicom.dataset.Dataset` instances. In order to do this,
    a validator is substituted for `type_constructor` when constructing the
    :class:`~pydicom.multival.MultiValue` super class.
    """

    def __init__(self, iterable: Iterable[Dataset] | None = None) -> None:
        """Initialize a list of :class:`~pydicom.dataset.Dataset`.

        Parameters
        ----------
        iterable : list-like of dataset.Dataset, optional
            An iterable object (e.g. :class:`list`, :class:`tuple`) containing
            :class:`~pydicom.dataset.Dataset`. If not used then an empty
            :class:`Sequence` is generated.
        """
        # We add this extra check to throw a relevant error. Without it, the
        # error will be simply that a Sequence must contain Datasets (since a
        # Dataset IS iterable). This error, however, doesn't inform the user
        # that the actual issue is that their Dataset needs to be INSIDE an
        # iterable object
        if isinstance(iterable, Dataset):
            raise TypeError("The Sequence constructor requires an iterable")

        # the parent dataset
        self._parent_dataset: weakref.ReferenceType[Dataset] | None = None

        # validate_dataset is used as a pseudo type_constructor
        self._list: list[Dataset] = []
        # If no inputs are provided, we create an empty Sequence
        super().__init__(validate_dataset, iterable or [])
        for ds in self:
            ds.parent_seq = self  # type: ignore
        self.is_undefined_length: bool

    def append(self, val: Dataset) -> None:  # type: ignore[override]
        """Append a :class:`~pydicom.dataset.Dataset` to the sequence."""
        super().append(val)
        val.parent_seq = self  # type: ignore

    def extend(self, val: Iterable[Dataset]) -> None:  # type: ignore[override]
        """Extend the :class:`~pydicom.sequence.Sequence` using an iterable
        of :class:`~pydicom.dataset.Dataset` instances.
        """
        if isinstance(val, Dataset):
            raise TypeError("An iterable of 'Dataset' is required")

        super().extend(val)
        for ds in val:
            ds.parent_seq = self  # type: ignore

    def __deepcopy__(self, memo: dict[int, Any] | None) -> "Sequence":
        cls = self.__class__
        copied = cls.__new__(cls)
        if memo is not None:
            memo[id(self)] = copied
        copied.__dict__.update(deepcopy(self.__dict__, memo))
        for ds in copied:
            ds.parent_seq = copied  # type:ignore
        return copied

    def __iadd__(  # type: ignore[override]
        self, other: Iterable[Dataset]
    ) -> MutableSequence[Dataset]:
        """Implement Sequence() += [Dataset()]."""
        if isinstance(other, Dataset):
            raise TypeError("An iterable of 'Dataset' is required")

        result = super().__iadd__(other)
        for ds in other:
            ds.parent_seq = self  # type: ignore

        return result

    def insert(self, position: int, val: Dataset) -> None:  # type: ignore[override]
        """Insert a :class:`~pydicom.dataset.Dataset` into the sequence."""
        super().insert(position, val)
        val.parent_seq = self  # type: ignore

    @property
    def parent_dataset(self) -> "weakref.ReferenceType[Dataset] | None":
        """Return a weak reference to the parent
        :class:`~pydicom.dataset.Dataset`.

        .. versionadded:: 2.4

            Returned value is a weak reference to the parent ``Dataset``.
        """
        return self._parent_dataset

    @parent_dataset.setter
    def parent_dataset(self, value: Dataset) -> None:
        """Set the parent :class:`~pydicom.dataset.Dataset`

        .. versionadded:: 2.4
        """
        if value != self._parent_dataset:
            self._parent_dataset = weakref.ref(value)

    @overload  # type: ignore[override]
    def __setitem__(self, idx: int, val: Dataset) -> None:
        pass  # pragma: no cover

    @overload
    def __setitem__(self, idx: slice, val: Iterable[Dataset]) -> None:
        pass  # pragma: no cover

    def __setitem__(self, idx: slice | int, val: Iterable[Dataset] | Dataset) -> None:
        """Set the parent :class:`~pydicom.dataset.Dataset` to the new
        :class:`Sequence` item
        """
        if isinstance(idx, slice):
            if isinstance(val, Dataset):
                raise TypeError("Can only assign an iterable of 'Dataset'")

            super().__setitem__(idx, val)
            for ds in val:
                ds.parent_seq = self  # type: ignore
        else:
            val = cast(Dataset, val)
            super().__setitem__(idx, val)
            val.parent_seq = self  # type: ignore

    def __str__(self) -> str:
        """String description of the Sequence."""
        return f"[{''.join([str(x) for x in self])}]"

    def __repr__(self) -> str:  # type: ignore[override]
        """String representation of the Sequence."""
        return f"<{self.__class__.__name__}, length {len(self)}>"

    def __getstate__(self) -> dict[str, Any]:
        if self.parent_dataset is not None:
            s = self.__dict__.copy()
            s["_parent_dataset"] = s["_parent_dataset"]()
            return s
        return self.__dict__

    # If recovering from a pickle, turn back into weak ref
    def __setstate__(self, state: dict[str, Any]) -> None:
        self.__dict__.update(state)
        if self.__dict__["_parent_dataset"] is not None:
            self.__dict__["_parent_dataset"] = weakref.ref(
                self.__dict__["_parent_dataset"]
            )
